On Tue, Aug 18, 2015 at 10:05 AM, Serge Pavlov <sepavl...@gmail.com> wrote:
> sepavloff added inline comments.
>
> ================
> Comment at: lib/AST/DeclBase.cpp:273
> @@ +272,3 @@
> + return true;
> + if (const CXXRecordDecl *ClassD = dyn_cast<CXXRecordDecl>(LDC))
> + return ClassD->isLocalClass() && !ClassD->isLambda();;
> ----------------
> rsmith wrote:
> > It's not necessary for this change, but to match its documentation this
> function should handle other kinds of `TagDecl` too (enums, C structs).
> Something like:
> >
> > do {
> > if (LDC->isFunctionOrMethod())
> > return true;
> > if (!isa<TagDecl>(LDC))
> > return false;
> > LDC = LDC->getLexicalParent();
> > } while (LDC);
> > return false;
> >
> > ... maybe?
> The proposed code recognizes lambda as lexically contained within a
> function. As a result, the following test starts to fail (obtained from
> CXX\expr\expr.prim\expr.prim.lambda\default-arguments.cpp):
> ```
> struct NoDefaultCtor {
> NoDefaultCtor(const NoDefaultCtor&); // expected-note{{candidate
> constructor}}
> ~NoDefaultCtor();
> };
>
> template<typename T>
> void defargs_in_template_unused(T t) {
> auto l1 = [](const T& value = T()) { };
> l1(t);
> }
>
> template void defargs_in_template_unused(NoDefaultCtor);
> ```
> because default value for lambda argument cannot be instantiated. It is
> not clear whether instantiation of the lambda default argument must always
> occur similar to DR1484. I couldn't find appropriate place in the standard.
> According to spirit it shouldn't as lambda is not a separate declaration
> but a part of instantiated content.
I agree. The default argument must be instantiated as part of instantiating
the surrounding function.
> If so 14.6.4.1p2 is more likely to be applied and the above test must
> pass.
>
The call operator of the lambda is neither a function template nor a member
function of a class template. The relevant rule is 14.7.1/1: "Within a
template declaration, a local class or enumeration and the members
of a local class are never considered to be entities that can be separately
instantiated (this includes their
default arguments, exception-specifications, and non-static data member
initializers, if any)." The lambda expression defines a local class, so its
members' default arguments are instantiated with the surrounding function.
> Maybe we need to rename `isLexicallyWithinFunctionOrMethod` to
> `shouldBeAlwaysInstantiated` or something like that to avoid
> misunderstanding?
>
>
>
> http://reviews.llvm.org/D11194
>
>
>
>
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